JavaPOS: claim method thread-safety.

Capabilities: useful in the same and different Java process.
It can not work with more than one instance of the same JavaPOS driver.

diff --git a/JavaPOS/KeyBoardDriver/src/main/java/de/javapos/example/hardware/KeyBoardDeviceLinux.java b/JavaPOS/KeyBoardDriver/src/main/java/de/javapos/example/hardware/KeyBoardDeviceLinux.java
index cf62ec6..d8e1d4d 100644 (file)
--- a/JavaPOS/KeyBoardDriver/src/main/java/de/javapos/example/hardware/KeyBoardDeviceLinux.java
+++ b/JavaPOS/KeyBoardDriver/src/main/java/de/javapos/example/hardware/KeyBoardDeviceLinux.java
@@ -12,10 +12,6 @@ import java.nio.channels.FileChannel;
 import java.nio.channels.FileLock;
 import java.nio.channels.OverlappingFileLockException;
 import java.util.concurrent.RejectedExecutionException;
-import java.util.concurrent.TimeUnit;
-import java.util.concurrent.locks.Lock;
-import java.util.concurrent.locks.ReentrantLock;
-
 import jpos.JposConst;
 import jpos.JposException;
 import org.apache.log4j.Logger;
@@ -36,15 +32,14 @@ public class KeyBoardDeviceLinux implements BaseKeyBoardDriver {
        //No me gusta nada esto, simplemente es para evitar mirar si thread es null la primera vez en el metodo enable...
        private Thread thread = new Thread ("KeyBoardDeviceLinux-Thread");
        private String deviceName;
-       @GuardedBy("claimLock") private FileChannel fileChannelLock;
+       @GuardedBy("this") private FileChannel fileChannelLock;
        @GuardedBy("this") private DataInputStream device;
-       @GuardedBy("claimLock") private volatile boolean isClaimed;
+       @GuardedBy("this") private boolean isClaimed;
        @GuardedBy("this") private boolean isEnabled;
        //Usando volatile porque cumplo las condiciones de uso. Ver Java Concurrency in Practice PAG????
        private volatile boolean autoDisable;
        private JposEventListener eventListener;
-       @GuardedBy("claimLock") private FileLock lock;
-       private Lock claimLock = new ReentrantLock(true);
+       @GuardedBy("this") private FileLock lock;
        
        @Override
        public boolean isOpened() {
@@ -64,53 +59,7 @@ public class KeyBoardDeviceLinux implements BaseKeyBoardDriver {
         * <b>Thread-safe</b>
         * </p>
         */
-       @Override
-       public void claim(int time) throws JposException {
-
-               //Using explicit Locks. Java Concurrency in Practice§13
-               //I want to attempt to acquire this lock without waiting for it forever when the timeout is not -1.
-               if (time == -1) {
-                       try {
-                               this.claimLock.lockInterruptibly();
-                               //Exclusive access code.
-                               try {
-                                       this.claimImplementation(time);
-                               } finally {
-                                       this.claimLock.unlock();
-                               }
-                       } catch (InterruptedException e) {
-                               //restore interrupt status.
-                               Thread.currentThread().interrupt();
-                               throw new JposException(JposConst.JPOS_E_CLAIMED, "Interrupt exception detected.", e);
-                       }
-               }
-               else {
-                       try {
-                               if (this.claimLock.tryLock(time, TimeUnit.MILLISECONDS)) {
-                                       //Exclusive access code.
-                                       try {
-                                               this.claimImplementation(time);
-                                       } finally {
-                                               this.claimLock.unlock();
-                                       }
-                               }
-                               else {
-                                       throw new JposException(JposConst.JPOS_E_TIMEOUT, "Timeout while trying to claim device.");
-                               }
-                       } catch (InterruptedException e) {
-                               Thread.currentThread().interrupt();
-                               throw new JposException(JposConst.JPOS_E_CLAIMED, "Interrupt exception detected.", e);
-                       }
-                       try {
-                               this.wait(250);
-                       } catch (InterruptedException e) {
-                               Thread.currentThread().interrupt();
-                               throw new JposException(JposConst.JPOS_E_CLAIMED, "Interrupt exception detected.", e);
-                       }
-               }
-       }
-
-       private void claimImplementation(int time) throws JposException {
+       public synchronized void claim(int time) throws JposException {
                FileLock lock = null;
                FileChannel fileChannelLock = null;
 
@@ -126,17 +75,32 @@ public class KeyBoardDeviceLinux implements BaseKeyBoardDriver {
                }
 
                if (time == -1) {
-                       try {
-                               //This method is not aware interrupt. :(
-                               lock = fileChannelLock.lock();
-                       //I do not like catching RunTimeExceptions but I have no choice...
-                       } catch (OverlappingFileLockException e) {
-                               closeFileLock(fileChannelLock);
-                               throw new JposException(JposConst.JPOS_E_CLAIMED, "More than one instances of the " +
-                                                                               "KeyBoardDeviceLinux JavaPOS driver.",e); 
-                       } catch (IOException e) {
-                               closeFileLock(fileChannelLock);
-                               throw new JposException(JposConst.JPOS_E_CLAIMED, "Error while trying to claim device.",e);
+                       //Espera activa. ¿Alguna idea de cómo hacer esto sin espera activa?  :(
+                       while(true) {
+                               try {
+                                       if ((lock = fileChannelLock.tryLock()) != null) {
+                                               break;
+                                       }
+                                       //Release monitor
+                                       this.wait(250);
+                               //I do not like catching RunTimeExceptions but I have no choice...
+                               } catch (OverlappingFileLockException e) {
+                                       closeFileLock(fileChannelLock);
+                                       logger.warn("File already locked or more than one instances of the " +
+                                                                       "KeyBoardDeviceLinux JavaPOS driver.",e);
+                                       //Nothing to do. File already locked (claimed device)
+                                       //or you are running more than one instances of this driver at the
+                                       //same time and in the same Java process, which is not supported.
+                                       return;
+                               } catch (IOException e) {
+                                       closeFileLock(fileChannelLock);
+                                       throw new JposException(JposConst.JPOS_E_CLAIMED, "Error while trying to claim device.",e);
+                               } catch(InterruptedException e) {
+                    closeFileLock(fileChannelLock);
+                    //restore interrupt status.
+                    Thread.currentThread().interrupt();
+                    throw new JposException(JposConst.JPOSERR, "Interrupt exception detected.", e);
+                }
                        }
                }
                else {
@@ -147,19 +111,24 @@ public class KeyBoardDeviceLinux implements BaseKeyBoardDriver {
                                        if ((lock = fileChannelLock.tryLock()) != null) {
                                                break;
                                        }
+                                       //Release monitor
                                        this.wait(250);
                                //I do not like catching RunTimeExceptions but I have no choice...
                                } catch (OverlappingFileLockException e) {
                                        closeFileLock(fileChannelLock);
-                                       throw new JposException(JposConst.JPOS_E_CLAIMED, "More than one instances of the " +
-                                                                                                                       "KeyBoardDeviceLinux JavaPOS driver.",e); 
+                                       logger.warn("File already locked or more than one instances of the " +
+                                                                       "KeyBoardDeviceLinux JavaPOS driver.",e);
+                                       //Nothing to do. File already locked (claimed device)
+                                       //or you are running more than one instances of this driver at the
+                                       //same time and in the same Java process, which is not supported.
+                                       return;
                                } catch (IOException e) {
                                        closeFileLock(fileChannelLock);
                                        throw new JposException(JposConst.JPOS_E_CLAIMED, "Error while trying to claim device.",e);    
                 } catch(InterruptedException e) {
                     closeFileLock(fileChannelLock);
                     //restore interrupt status.
-                       Thread.currentThread().interrupt();
+                    Thread.currentThread().interrupt();
                     throw new JposException(JposConst.JPOSERR, "Interrupt exception detected.", e);
                 }
                        } while(System.nanoTime() <= lastTime);
@@ -192,23 +161,7 @@ public class KeyBoardDeviceLinux implements BaseKeyBoardDriver {
         * </p>
         */
        @Override
-       public void release() throws JposException {
-               try {
-                       this.claimLock.lockInterruptibly();
-                       try {
-                               //Exclusive access code.
-                               this.releaseImplementation();
-                       } finally {
-                               this.claimLock.unlock();
-                       }
-               } catch (InterruptedException e) {
-                       //restore interrupt status.
-                       Thread.currentThread().interrupt();
-                       throw new JposException(JposConst.JPOS_E_CLAIMED, "Interrupt exception detected.", e);
-               }
-       }
-
-       private void releaseImplementation() throws JposException {
+       public synchronized void release() throws JposException {
 
                if (!this.isClaimed) {
                        return;
@@ -225,7 +178,7 @@ public class KeyBoardDeviceLinux implements BaseKeyBoardDriver {
        }
 
        @Override
-       public boolean isClaimed() {
+       public synchronized boolean isClaimed() {
                return this.isClaimed;
        }